Filtration face masks (hereinafter masks) are used in a wide variety of applications when it is desired to protect a human's respiratory system from particles suspended in the air or from unpleasant or noxious gases.
Wearer comfort is paramount to overcome the frequently encountered resistance to use. In addition to the comfort derived from a proper fit to a human face, it is desirable that a mask require a minimum to effort to draw air in through the filter media. This is referred to as the pressure drop across a mask, or breathing resistance.
To reach higher levels of filter efficiency, more or thicker layers of filter material are typically used. If the filter area is held constant the addition of more layers of filter material raises the pressure drop across a mask. Provision of high efficiency face masks has been limited by the fact that the thicker filtration layers needed for such performance leave conventionally designated face masks with unacceptable pressure drops. Formation of face masks with a larger filter material surface area typically lowers the pressure drop, and masks having an increased filter surface area over that of a generally cup-like shaped mask are described in, for example, U.S. Pat. Nos. 4,248,220 and 4,417,575, and EPO application No. 149,590 A3. Masks disclosed in these references suffer from difficulties in manufacture and/or poor fit to the wearer's face. In addition, prior art attempts at increasing surface area have included the use of sharp pleats or folds in the filter material. While this is acceptable for thin, paper-like filter material it will not work when a thick filter material is used.
It is, therefore, highly desirable to provide a mask which has an increased filter media surface area over that of a cup-like shaped mask without the use of sharp pleats or folds, is exceptionally easy to manufacture, and is comfortable and firmly fitting on the face of a typical human wearer.